PROJECT SUMMARY/ABSTRACT Breastfeeding is associated with a variety of positive health outcomes in children and is recommended exclusively for the first 6 months of life; however, 50-70% of infants in the U.S. are formula-fed. The goal of the study is to understand the regulators that drive breastmilk-associated advantages in terms of gut development and immune function. It has been suggested that breastfed infants have advanced immune system development compared to formula-fed infants, but the underlying mechanisms remain to be fully elucidated, in part due to the challenges associated with It is well known that dietary factors in breastmilk and formulas can alter gut microbiota composition. Other questions, however, have not been answered: (1) Do the microbiota alone shape gut development and subsequent immune function in infants, and what are the molecular signals involved? (2) Do breastfed children have better immune responses to infections? In order to understand and address these questions, the Project Leader has developed a piglet model of infant formula feeding. Preliminary data demonstrated that gastrointestinal tract development and gut associated lymphoid tissue is highly developed in breast milk fed piglets (sow-fed) in comparison to formula-fed piglets. The differential effects of early diet on gastrointestinal development and function are only partially characterized, and the long-term health consequences and the mechanisms by which these occur are not yet established. The study aims to utilize the pig model of formula feeding to determine the effects of early diet on gastrointestinal development and function and to what extent these effects are secondary to differences in the gut microbiota and also differences in immune function at local and systemic levels. The study will provide a unique dataset and is an exceptional resource to investigate the consequences of early infant feeding, including the elucidation of the effects of early diet. The ultimate goal will be to improve infant formula by adding components that lead to similar outcomes as seen in breastfed, or to alter microbiota in the form of prebiotics and probiotics to help boost the immune system and GI tract development in infants. specimen collection and experimental intervention in human newborns and infants.